Conductive inks can be formed into wiring elements by film formation through coating, and this allows a considerable reduction in cost and environmental load as compared to the case of conventional vacuum processes. Conductive inks have therefore been ranked as industrially very important technical means, and the development of their materials has been actively pursued.
For example, there have recently been developed metal nanoparticle inks that exhibit a high electrical conductivity of 10−5 Ω·cm or less when sintered at a temperature of 150° C. or lower. The use of such inks allows various electronic circuits to be formed even on plastic films having low heat resistance.
In forming wiring elements of an electronic circuit, it may be necessary to form a contact hole for providing electrical contact between a lower wiring element formed on a substrate and an upper wiring element insulated by an insulating layer formed from a resin or the like on the lower wiring element.
In the case of conventional silicon semiconductor devices, the formation of a contact hole is accomplished using a lithography technique and an etching technique. An example of conventionally-used methods is one in which a resist pattern is formed by photolithography and then a contact hole is formed, for example, by dry etching using a reactive plasma gas. However, combining such a method using dry etching with a printing device poses difficulty in terms of cost since the dry etching is a vacuum process.
As for an example of contact hole formation methods free of any vacuum process and applicable to printing devices, Patent Literature 1 discloses a method that uses laser ablation to form a through hole (contact hole).
In addition, Patent Literature 2 discloses a method in which a conductive ink is first applied onto a lower wiring pattern in such a manner that the conductive ink will form island-shaped projections protruding from an insulating layer, and then the insulating layer and an upper wiring element are stacked.
As for a method for forming a wiring by printing, Patent Literature 3 proposes a method that uses a metal nanoparticle ink and in which the ink is sintered by light irradiation with a flash lamp.